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Monday, August 21, 2017

SPACE CADETS / CASE OF THE DISAPPEARING MOON

Here’s what you’ll see today if you’re among those along the path of totality, where the eclipse will be the darkest and longest.Researchers from the National Solar Observatory Integrated Synoptic Program predict the structure of the solar corona for the 2017, total solar eclipse. The field lines of a solar coronal magnetic model shown in the image are based on measurements taken one solar rotation, or 27.2753 Earth days, before the total solar eclipse.

ALONG THE PATH OF TOTALITY

GUEST BLOG / By
Samantha Mathewson, Space.com contributing writer--With the Aug. 21 total
solar eclipse finally here, astronomers have revealed what the sun's
outer atmosphere is likely to look like as the sun disappears behind the moon.

The rare eclipse will sweep across the continental U.S.
from Oregon to South Carolina along a stretch of land about 70 miles (113
kilometers) wide. Skywatchers within this path will experience totality, when
the moon appears to move directly in front of the solar disk and casts a long
shadow on Earth. Viewers outside of the path of totality will still experience
a partial solar eclipse.

During a total solar eclipse, skywatchers have the
opportunity to see the sun's glowing outer atmosphere, known as the corona. The
jets and streamers present in the corona become visible because the moon blots
out much of the bright light of the sun's disk, which typically overwhelms the
light from the corona.

The corona is more than a glowing halo of light. It is
incredibly hot — it can reach temperatures of 3.5 million degrees Kelvin (3.49
million degrees Celsius or 6.29 million degrees Fahrenheit) — and has an
intricate structure created by the sun's magnetic-field lines.

Using measurements from the National Solar Observatory
Integrated Synoptic Program (NSO/NISP), astronomers were able to model the
shape of the solar coronal magnetic field as of July 25, which represents one
solar rotation, or 27.2753 Earth days, before the Aug. 21 total solar eclipse.

Here's what was predicted a month ago: "Since we are exactly one solar rotation away from the
solar eclipse, we're able to use today's observations to predict the structure
of the corona on Aug. 21st," Gordon Petrie, an astronomer from the NSO,
said in a statement in early August. "The corona is not likely to change too much between
now and the eclipse, unless we get lucky and a large active region
appears!"

"We expect to see faint, straight structures protruding
from the north and south poles of the sun — these are the polar plumes,"
Petrie added. "We will be able to see brighter bulbs of material closer to
the equator — these are called helmet streamers."

Electric currents inside the sun generate a magnetic field
that changes over time, depending on where the sun is in its 11-year activity
cycle. Astronomers are able to trace the magnetic fields of the corona by
observing the superheated gases present in the sun's atmosphere. Astronomers
compare this technique to "the middle-school experiment where you sprinkle
iron filings over a bar magnet to get a butterfly shape," according to the
statement.

"The corona changes its shape over time, and looks
drastically different during solar maximum compared to solar minimum,"
David Boboltz, the National Science Foundation's program officer for the NSO,
said in the statement. "During solar maximum, such as the 2012 eclipse,
the corona looks like a spiky ring around the entire sun. In contrast, a solar
minimum eclipse such as the one this month, will have lots of complexity near
the equator but will be drastically different near the north and south poles of
the sun."

While skywatchers in
the path of totality will experience no more than 2 minutes and 40 seconds of
darkness in any one location, scientists will be able to combine observations
taken of the sun's corona over the course of 90 minutes — the time it takes the
moon's dark shadow to travel from the West Coast to the East Coast. This will
allow astronomers to further study the corona and its structure.

What's more, the NSO is also helping to build the Daniel K.
Inouye Solar Telescope (DKIST) on the Hawaiian island of Maui, which will allow
scientists to measure the magnetic fields in the solar corona directly for the
first time, according to the statement.

"The solar corona is largely an enigma," Valentin
Pillet, director of the NSO, said in the statement. "For now, the best we
can do is compare high resolution images of the solar corona, such as those
we'll obtain during the eclipse, to our theoretical models. But DKIST will
allow us to actually measure the magnetic fields in the corona. This will be
revolutionary in the field of solar physics."

Samantha Mathewson
joined Space.com as an intern in the summer of 2016. She received a B.A. in
Journalism and Environmental Science at the University of New Haven, in
Connecticut. Previously, her work has been published in Nature World News. When
not writing or reading about science, Samantha enjoys traveling to new places
and taking photos! You can follow her on Twitter @Sam_Ashley13.